Isotopes are any of several different forms of an element each having a different atomic mass (mass number). The term “isotope”, coined by British chemist F. Soddy in 1913, comes from the Greek isos “equal”+topos “place,” because despite the different atomic weights, the various forms of an element occupy the same place on the periodic table.
Generally, the chemical properties of an element depend on the number of protons, that is, the atomic number. Isotopes of an element have nuclei having the same number of protons (the same atomic number) but different numbers of neutrons. Therefore, isotopes have different mass numbers, which indicate the total number of nucleons—the number of protons plus neutrons.
For example, oxygen occurs in nature as three different isotopes, each with 8 protons. The most common isotope is 16O (8 protons, 8 neutrons), which constitutes more than 99% of all oxygen atoms on earth. There is also the rare isotope 18O (10 neutrons) and the even rarer isotope 17O (9 neutrons). Nitrogen exists as two stable isotopes, 14N and 15N, in nature. Naturally occurring uranium is composed of three major isotopes, uranium-238, uranium-235, and uranium-234.
Because there are the same numbers of electrons as protons in an element, isotopes of an element are identical in the number of electrons. Approximately 90 elements exist in nature, and there are as many as about 300 naturally occurring isotopes, with an average of 3 isotopes per element. In fact, tin (Sn) is the element with the greatest number of stable isotopes (ten), and cadmium has the second highest number of isotopes (eight) while there are elements that exist as only one isotope in nature, such as beryllium, fluorine, sodium and bismuth.
There is no general rule for relationship between a naturally occurring element and the number of stable isotopes thereof. However, it has been observed that most of the elements that have odd atomic numbers each have two or fewer isotopes, whereas individual elements with even atomic numbers have relatively many isotopes. A naturally occurring element is a mixture of isotopes with almost the same ratios therebetween or thereamong in any sample of the earth. In general, the atomic weight of an element is the average of the atomic masses of all the chemical element's isotopes as found in a particular environment, weighted by isotopic abundance. The reason why a majority of atomic weights are not integers or near-integers but decimals is that most elements are assemblages of isotopes. For a short-hand designation of different isotopes (also called nuclides), the mass number (number of nucleons) is written in the right position or in the upper left corner of the chemical symbol, like oxygen-16, 16O, nitrogen-14 14N, uranium-235 235U, etc. Particularly as for hydrogen isotopes, specific names are given thereto, such as protium for H-1, deuterium for H-2, and tritium for H-3.
Recent studies have showed that the oxygen isotope 18O is toxic to organisms. Deuterium 2H in the form of D2O was found to have 92% inhibitory activity against microorganisms and to kill rats at a rate of 99.5% within 5 days.
High prevalence rates of cancer are reported in radioactive contamination area, implying that persons excessively exposed to radioactive radiation may increase in isotope level in their bodies and may be liable to affliction with cancer.
Leading to the present invention, intensive and thorough research into the treatment and diagnosis of cancer, conducted by the present inventor, resulted in the finding that cancer can be caused with a change in blood isotope level and that the incidence and kind of cancer can be diagnosed through the quantitative analysis of blood or tissue isotopes.